Plant and animal life had it rough 250 million years ago. As if to add insult to injury, the end-Permian mass extinction was quickly followed by yet another mass extinction, what's called the Smithian-Spathian extinction. New research suggests that the Earth got excruciatingly hot during this period, creating a veritable 'dead zone' in tropical areas, what forced the remaining animal life to head to the poles. And it lasted for nearly 5 million years.

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According to research done by Yadong Sun and Paul Wignall of the University of Leeds, UK, this was hottest era on Earth since it cooled down from its initial molten formation. Their study has reset notions of just how hot our planet can get — a disturbing bit of insight that could reset current models of climate change on Earth.

The Smithian-Spathian extinction was time that characterized the shift from the Permian era to the Triassic, just before the emergence of the dinosaurs. By this point, the mysterious Permian Extinction had reduced the life on Earth to a select group of insects, plants, marine life (like fish, coral, sea lilies, and ichthyosaurs), and terrestrial animals (like insects and the reptilian tetrapod).

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Sun and Wignall's research indicates that during this time, the heat at the tropical regions reached an astounding 50 to 60°C (122°F to 140°F) on land, while the waters at the surface reached 40°C (104°F). They were surprised to discover that the water could get that hot; previous estimates assumed that sea-surface temperatures could not surpass 30°C (86°F). Moreover, at 40°C, most marine life dies and photosynthesis stops.

A paleogeographic reconstruction of the Early Triassic world (Smithian substage) around 252 to 247 million years ago, showing a ‘dead zone' in the tropics. Marine reptiles (ichthyosaurs), terrestrial tetrapods and fish almost exclusively occurred in higher latitudes (>30 °N and >40 °S) with rare exceptions. Credit: Yadong Sun, University of Leeds.

And indeed, life had no choice but to react to this heat. It's suspected that marine life swam to the polar regions to keep cool. Similarly, terrestrial animals also headed to the extreme north and south. Back then, the mega-continent Pangea existed, making Antarctica/Australia and Siberia likely areas for re-habitation.

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Meanwhile, the tropical regions would have been bizarre places to visit. These areas would have been very wet, but with very few plants growing — only shrubs and ferns. These ares would have been devoid of most terrestrial creatures. And in the waters, only shellfish would have stuck around.

What happened? Essentially, the superhot Earth was caused by a breakdown in global carbon cycling. Normally, plants help regulate temperature by absorbing CO2 and burning it as dead plant matter. But without plants, the CO2 levels rose unchecked, causing a spike in temperatures. Specifically, the researchers estimate that at least 12×103 gigatons of isotopically depleted carbon as methane was injected into the atmosphere.

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To reach this conclusion, the scientists collected data from over 15,000 conodonts (tiny teeth of eel-like fishes). By analyzing the isotopes of oxygen in these remnants, they were able to determine the temperature levels hundreds of millions of years ago. You can read the entire study at Science.